The invention relates to a resonator device, in particular a microwave resonator device, for testing a material quantity and especially a material flow in the tobacco-processing industry for the existence of at least one foreign substance and/or for detecting the weight, density and/or humidity level of the material or material flow. The resonator device is provided with at least one resonator housing and at least one opening in each resonator housing for the material or material flow to pass through.
The invention furthermore relates to a corresponding measuring device, especially a microwave measuring device, as well as a measuring system, in particular a microwave measuring system, for testing a material quantity and especially a material flow in the tobacco-processing industry for the existence of at least one foreign substance and/or for detecting the weight, density and/or humidity level of the material. Such a measuring device comprises at least one resonator housing, inside of which an electromagnetic field can be generated and which has at least one through opening for the material.
Finally, the invention relates to a method for testing a material for the existence of at least one foreign substance and/or for detecting the weight, density and/or humidity level of the material.
A corresponding resonator device or resonator housing for microwaves is known from German Patent No. 198 54 550 A1 commonly owned by the present assignee. This document discloses a resonator housing for the tobacco-processing industry, through which a rope of tobacco is moved and is subjected to microwaves for the purpose of detecting the weight and/or humidity level of the rope material. The purpose of this resonator housing is to improve the measuring accuracy and, if necessary, the measuring sensitivity when detecting the weight and/or humidity level of filler materials for ropes in the tobacco-processing industry. According to German Patent No. 198 54 550 A1, this is achieved by producing the housing at least in part from a material with a low expansion coefficient, so that with a corresponding fluctuation in the temperature, the housing essentially retains the same shape. It also improves the measuring accuracy if the resonator housing temperature is controlled to be at a constant value. Finally, it is advantageous according to the aforementioned reference if the interior housing walls are at least partially coated with a corrosion-resistant metal or consist of such a metal. The measuring accuracy for detecting the weight and/or humidity level for the aforementioned materials can be improved considerably in this way.
German Patent No. 101 00 664.0 also commonly owned by the present assignee, furthermore discloses a method for testing a production material or a material quantity primarily containing a production material, wherein the material is tested for the existence of a foreign substance. A microwave field is generated for this, the material is moved into the effective range of the microwave field and its influence on the microwave field is analyzed, wherein the actual values of a first and a second characteristic variable of the microwave field are measured simultaneously. A reliable value range is specified for these actual values and these are checked to determine whether the actual values are in the reliable range. A signal is generated if the actual values are outside of the reliable value range. For the purpose of this invention, the variable for a microwave field includes real variables of the generated microwave field, such as amplitude and phase, as well as variables of the components for guiding a microwave field, e.g. the resonance frequency and the band width of a resonator in which the microwave field propagates.
With the known measuring method, the goods to be measured are moved through the field of a resonator, wherein the dielectric properties of the goods to be measured change the field. By measuring the change in the resonance properties or the field, it is possible to determine the weight, density and humidity level as well as to detect foreign substances. However, it is difficult to detect very small foreign substances or to achieve a relatively exact local resolution. In particular the position of the foreign substance relative to the field orientation determines the measuring accuracy.